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CODESYS Example: ModbusTCP-RTU-Master

Introduction​

This tutorial demonstrates how to configure Modbus TCP and Modbus RTU masters on a RevPi Connect+ with CODESYS Control CODESYS Control for Linux ARM or ARM64 . The application reads the holding registers (0–9) of connected Modbus slaves and writes their values back to holding registers (10–19).

Prerequisites​

Hardware Requirements​

  • RevPi Connect+
  • One Modbus TCP slave
  • One Modbus RTU slave

Software Requirements​

  • CODESYS Development System installed on your PC

Preparation​

Hardware Setup:​

Tipp: For detailed instructions about how to set up your system, refer to the Getting Started guide.

Software Setup:​

note: To ensure a compatible system with suitable software, please refer the following links:

Overview​

The device tree in CODESYS is configured with:

  • Modbus TCP Master: Reads and writes to a TCP slave device.
  • Modbus RTU Master: Communicates with a serial RTU slave device.
  • POU_Modbus: Handles the application logic for reading and writing data.

Project Setting

Adapting for RevPi Core or Compact

To adapt the project for RevPi Core or RevPi Compact:

▷ Right-click on RevPi Connect in the CODESYS device tree.

▷ Select Update device.

▷ Choose RevPi Core or RevPi Compact as the replacement and rename the device accordingly.

Step 1: Configuring Modbus RTU Serial Port​

For RevPi Connect or RevPi Core:​

  1. Edit the configuration file:

    sudo nano /etc/CODESYSControl_User

  2. Add the following line:

    [SysCom]  
    Linux.Devicefile=/dev/ttyUSB

  3. Map the COM ports in CODESYS as follows:

    • /dev/ttyUSB0 → COM port 1
    • /dev/ttyUSB1 → COM port 2
    • /dev/ttyUSBn → COM port n

    If an extra USB-485 converter is connected, the correct COM port has to be identified.

    Project Setting

For RevPi Compact:​

  • Default RS485 Port:
    ▷ Edit /etc/CODESYSControl_User and add: 
    [SysCom]  
    Linux.Devicefile=/dev/ttyAMA
  • Using USB-485 Converter:
    ▷ Add the following line instead: 
    [SysCom]  
    Linux.Devicefile=/dev/ttyUSB

Step 2: Configuring Modbus RTU Slave​

Project Setting

  1. Set up the RTU slave with:
    • Channel 1: Read Holding Registers
    • Channel 2: Write Multiple Registers

Project Setting

  1. Ensure the default values for the first 10 holding registers are 12.

Project Setting

  1. Map these channels in the POU_Modbus logic for application-level access.

Project Setting

Step 3: Configuring Modbus TCP Slave​

  1. Specify the Modbus TCP Slave Address in the CODESYS configuration.

Project Setting

  1. Use the same mapping logic as Modbus RTU for holding registers 0–9 and 10–19.

Step 4: Simulating Modbus Slaves​

To simulate Modbus TCP and RTU slaves, use ModRSsim2:

  • Download the application from ModRSsim2 on SourceForge.
  • Configure Modbus TCP/RTU slaves to have holding registers:
    • 40001–40010 for source data
    • 40010–40020 for destination data

Project Setting

Project Setting

Step 5: Deploy and Test​

  1. Download the compiled project to the RevPi device.
  2. Run the application on your RevPi Base Module.
  3. Verify that:
    • Data is correctly read from holding registers 0–9.
    • Data is written back to holding registers 10–19.

Notes​

  • Default RTU Slave Configuration: Ensure that slaves are set with unique IDs and consistent communication settings.
  • Debugging: Use CODESYS monitoring tools to verify the real-time data exchange between masters and slaves.
  • Simulation: Use ModRSsim2 for testing before connecting physical devices.

This setup allows Modbus TCP and RTU masters to operate simultaneously, enabling robust data exchange with Modbus-enabled devices.